Two wire follow-up system



Nov. 21, 1950 Filed Jan. 29, 1948 M. N.'YARDENY ETAL TWO WIRE FOLLOW-UP SYSTEM 2 Sheets-Sheet 2 Patented Nov. 21, 1950 TWO WIRE FOLLOW-UP SYSTEM Michel N. Yardeny, New York, Robert Bernas, Bronx, and Simon Goldberg, New York, N. Y.; said Bernas and said Goldberg assignors to said Yardeny Application January 29, 1948, Serial No. 5,064

8 Claims.

This invention relates to electric control apparatus to control an electric motor for placing a load in any desired position and stopping the load motor when the load is placed in the selected position.

In control apparatus of the general type above referred to, the control means are usually united in a transmitter located at a control point, while the load and the load motor are united in a receiver located at a remote point. The transmitter and the receiver are frequently separated by a considerable distance. As a result, the required signal transmitting means between the transmitter and the receiver are rather expensive and difiicult to keep in good repair.

One of the objects of the invention is to provide a novel and improved control apparatus in which the transmitter and receiver are connected by no more than two electric signal transmitting means, thereby substantially reducing the number of transmitting means, as hitherto required for control apparatus of the general type above referred to.

Another object of the invention is to provide a novel combination of a control apparatus of the general type above referred to with means to transmit signals received at the remote point to the control point and to energize these means through electric transmitting means that are employed to connect the transmitter with the receiver.

Another object of the invention is to provide a novel and improved apparatus of the general type above referred to, including a back indicator which is energized through the electric transmitting means that serve to connect th transmitter and the receiver, thereby attaining a further reduction of the electric transmitting means required for operation of the control apparatus.

The term electric signal transmitting means as herein sometimes used is intended to refer to and to include both physical connections, such as wires or conductors, and wireless connections such as radio channels.

Other and further objects, features and advantages of the invention will be pointed out in the subsequent description and in the appended claims forming part of the application.

Thi application is a continuation in part of our copending application Ser. No. 711,110 filed Nov. 20, 1946, now abandoned.

On the accompanying drawings several now preferred embodiments of a control apparatus according to the invention are shown by way of illustration and not by way of limitation.

In the drawings:

invention including a transmitter employing independently movable control members, and

Fig. 2 is a modification of the control apparatus including a transmitter producing current impulses as control signals.

Referring now to Fig. 1 of the drawings more in detail, the control apparatu consists of a transmitter generally designated T and a receiver generally designated R. The transmitter, located at a control point, serves to control the position of a load located at a remote point. There are also provided a back-indicator to indicate the position of the load at the control point and means to transmit signals received at the receiver to the transmitter.

More in detail, the transmitter includes a control unit, generally designated ID. This control unit comprises two electrically conductive segments l l and I2 supported on a rotatably mounted insulation disc l3 and separated by a gap l4. Segment II is electrically connected to a slip ring I5 and segment l2 to a slip ring l6, both slip rings being also supported on insulation disc [3. The disc is connected by gears l1 and I8 and transmission means l9 to a pilot motor 20. Segments II and I2 are slidably engaged by a contact element 2| of a rotatable contact arm 22 mounted co-axially with disk 13. Contact element 2| is so designed that it can either bridge gap M (as shown on the drawings) or is disengaged from both contact segments when occupying gap I4. A knob 23 serves to rotate contact arm 22, either directly or through a reduction ear. The contact arm is connected by a lead 25 to one terminal of an A. C. or D. C. source of current 26. Slip ring I5 is connected by a lead 21 to the outer terminal of a field winding 28, and slip ring [5 is connected by a lead 29 to the outer terminal of a second field winding 30. The inner terminals of the field windings are joined by a lead 3| which is connected by a lead 32 to one terminal of the armature 33 of pilot motor 20, the other terminal of the motor armature being connected by a lead 34 to the second terminal of source of current 26. The two field windings serve to reverse the direction of motor rotation and may also be employed to brake the motor electrodynamically. Lead 21 is connected by a lead 35 to one coil terminal of a relay 36 and lead 29 is connected by a lead 31 to one coil terminal of a second relay 38. The other coil terminals of the relays are joined by a lead 39 which in turn is connected by a lead 40 to supply lead 34. Relay 36 controls an armature 4| which engages a contact 42 when the relay is energized and a contact 43 when the relay is de-energized. Similarly, relay 38 controls an armature 44 which engages a contact 45 when the relay is energized and a contact 46 when the relay is deenergized. Contacts 42 and 45 are connected by leads 47 and 48 respectively to a terminal I20 of an oscillator 50 of conventional design connected by leads 49,

49 to source of current 26 or a separate source Contacts 43 and 46 are connected by of current. leads 5I and 52 respectively to another terminal I2I of the oscillator. Leads5I and 52 include capacitors 53 and 5 3 respectively, serving as tuning capacitors of the oscillator. Oscillator 50 is so constructed that it is is capable of producing several difierent frequencies, for instance frequencies f1 or f2, depending on whether capacitor 53 or 54 is connected across the terminals I20 or I2I. The output side of the oscillator is connected by leads 55 and 58 respectively with two leads 57 and 58 which serve to connect the transmitter of the control apparatus with the receiver. Leads 5? and 58 are connected by leads 59 and 60 respectively to a selective amplifier M of conventional design which is tuned to frequency f1 and by leads 82 and 63 respectively to a second selective amplifier 64 of conventional design, tuned to the frequency f2. The amplifiers are connected by leads 8 and 8' to a source of current 16. Amplifier 6I is connected by leads 65 and 66 respectively to the coil terminals of a relay 61, and similarly, amplifier 84 is connected by leads 68 and 69 respectively to the coil terminals of a relay I8. Relay 61 controls an armature H which engages a contact 72 when amplifier BI is energized. Similarly relay I controls an armature I3 which engages a contact I4 when amplifier 84 is energized. Armatures "II and I3 are connected by a lead 15 to one terminal of source of current I6 or a separate source of current. Contacts I2 and I4 are connected by leads TI and I8 respectively to the outer terminals of reversing field windings I9 and 30 respectively of a load motor, generally designated 8|. The inner terminals of the. field windings are joined and connected by a lead 82 to one terminal of motor armature 83 of the load motor, the other terminal of the motor armature being connected by a lead 84 to the second terminal of source of current 16. Motor 8| moves a load 85. by means of suitable transmission means 86 which may include gearing 81. Load 85 may consist of any suitable device or element and include a pointer 88 coasting with a calibrated scale (not shown).

Pilot motor 28 may be a small motor just sufiicient to operate control unit I E], whereas load motor 8I may be a powerful motor suitable to move a heavy load. Various types of motors can be employed as pilot motor and load motor respectively, including motors which will operate at different speed, such as non-synchronous motors. As a result, the control unit of the transmitter permits control of the operation of the load motor, as will be more fully described hereinafter, but the position of the pilot motor and hence of contact arm 22 may or may not be proportional to the position of the load. Consequently, indicating means are required to back-indicate the position of the load to the control point.

As previously mentioned, one of the objects of the. invention is a novel and improved back-indicating means which makes use of the two leads and 58 connecting the transmitter with the receiver.

According to a further object of the invention, the same leads 5? and 58 are employed to transmit signals, audible or non-audible, from the remote point to the control point.

For these purposes, lead 51, at the remote point, is connected by a lead 90 to the wiper 92 of a potentiometer 83 which in turn is connected by leads 94 and 95, respectively, to a D. C. source of current 96. Lead 90 is further connected by a lead 91 through a capacitor 98 and leads 85, 84 to the minus terminal of the source of currents 96, and by a lead I00 to one terminal of the secondary H of a transformer, generally designated I02. Lead 58 is connected by a lead I83 and low pass filter ill to the other terminal of secondary NH. The primary I04 of the transformer is connected to receive A. C. signals, produced for instance by the output of a radio receiver 89.

Wiper arm 92 of the potentiometer is operatively connected by suitable transmission means I05 to load 85 so that the position of the wiper arm of potentiometer 93 is alway indicative of the load position.

At the control point,lead 5! is connected by a lead I06 and a low pass filter I8! to one terminal of a D. C. measuring instrument I08. This instrument has a pointer I09 coacting with a scale IIO calibrated to indicate the positions of lead 85, as will be more fully explained hereinafter. The other terminal of meter I08 is connected by a lead I I I to one terminal of the primary I I2, of a. transformer generally designated I I3, the other terminal of primary II 2 being connected by a lead II4 through low pass filter I81 to lead 58. A capacitor [I5 is connected by a lead Hi? to the terminals of meter I 08. The A. C. impedance of this capacitor is so selected that it is small in comparison with the A. C. impedance of meter I08 so that the capacitor will operate as a bypass, allowing A, C. to vflow through the capacitor, whereas D. C. will flow through the meter. The secondary I I! of transformer I I3 is connected to an audio amplifier I I8 which serves to reproduce at the control point signals received by transformer I02 at the remote point.

Low pass filter 9| is so designed that it will pass signals received by transformer I02 but will'block signals having a frequency f1 or f2, thereby eliminating any influence. of signals having such frequency upon the operation of amplifiers BI and 64. Similarly low pass filter I0! is so designed that it will prevent signals having a frequency f1 or f2 and produced by oscillator 50 to reach audio amplifier II8.

The operation of the control apparatus according to Fig. 1- is as-follows:

When contact element 2! engages segments I I and I2, energizing circuits are closed for both field windings 28 and 38. The-circuit of winding 28 may be traced as follows: from one terminal of source of current 25. by lead 25, contact arm 22, contact element 2!, segment II, slip ring I5, lead 21, winding 28, leads 3! and 32, armature 33 and lead 34 back to the other terminal of source of current 28. The circuit for winding3!) can be similarly traced through segment I2. As a result, both field windings are energized in opposition, thereby braking motor 29 electro-dynamically. In addition, energizing circuits are closed for both relays 38 and 3 8. The circuit of relay 3% may be traced from lead 2? by. lead 35, coil 36, leads 39 and 40 back to lead 34. The circuit of relay 38. may be similarly traced. Consequently, both relays will attract their respectivearmatures M and 44, so that oscillator 50 remains inoperative. V

As will be evident from the previous explanation, a similar result can be obtained by arranging contact element 2I and gap I4 in such a manner that contact element 2I is disconnected from both segments when the gap isin alignment with the contact element. With such arrangements, motor 20 and both relays 36 and 38 will be disconnected. It should further be noted in this connection that it is quite practical and wellknown in the art to interpose a relay system between motor 20 and the segments which relay system is controlled by the relative position of segments II and I2 and contact element 22 and in turn controls the operation of pilot motor 20.

Let it now be assumed that it is desired to displace load 05 in counter-clockwise .direction. For this purpose contact arm is turned towards the left by means of knob 23, thereby placing contact element 2| in engagement with segment II only. As a result, field winding 30 is deenergized while field winding 28 remains energized through the circuit as previously traced. Consequently, pilot motor 20 rotates disk I3 in a direction selected to cause gap I4 to follow the displaced contact arm 22.

The displacement of the contact arm further causes relay 38 to be de-energized so that this relay releases its armature 44 which now engages contact 43, thereby closing a capacitance circuit for oscillator 50 which may be traced as follows:

from oscillator 50 by lead 41, contact 42, arma-' ture 4|, armature 44, contact 46, lead 52 tuning capacitor 54 and lead 5I back to oscillator 50. The oscillator is now energized to oscillate frequency i1 or f2, say frequency f1, which is transmitted by leads 51, 58 and leads 59, B to selective amplifier SI which in turn energizes contact 12, thereby closing a circuit for load motor 8| which may be traced as follows: from one terminal of source of current 10 by lead 15, armature 1I, contact 12, lead 11, field winding 19, lead 82, motor armature 83 and lead 84 back to the other terminal of the source of current 16. As aresult, motor 8! is energized to rotate in a direction as determined by the displacement of contact arm 22.

When now gap I4 catches up with contact arm 22 and is again bridged by contact element 2I, pilot motor 20 is stopped by the energization of both field windings 28 and 30, as previously explained, and load motor BI is also stopped, as now both relays 35 and 38 are again energized, thereby disconnecting the tuning circuit of oscillator 50.

It will be evident that the operation of the control apparatus is similar when contact arm 22 is placed in engagement with contact segment I2. In this case, oscillator 50 is energized to produce frequency f2, and pilot motor 20 and load motor 8I are connected to rotate in the opposite direction.

Load motor 8|, when operative, rotates pointer 88 of load 85 correspondingly so that the position of load and pointer 88 will be controlled by the displacement of contact arm 22. However, the position of the load and the pointer do not necessarily correspond to the angular displacement of contact arm 22, as pilot motor 20 and load motor 8| may rotate at different speeds or difi'erent ratios of transmission may be provided between the motors and the parts rotated thereby. Consequently, as previously mentioned, back-indicating means must be provided, the operation of which will now be described. As will be apparent from the drawing, the location of the load causes wiper arm 92 of potentiometer 93 to be rotated correspondingly. As a result, the direct current energizing D. C. meter I08 will be varied accordingly. The energizing circuit of the meter may be traced as follows: from wiper arm 92 by lead 90, low pass filter 9|, leads 90, 51, low pass filter I01, meter 00, lead III, primary Il2, lead II4, low pass filter I01, leads 58, I03, low pass filter 9|, secondary IOI, leads 99, 94 and resistance 93. As a result, pointer I09 of meter I08 will always indicate the position of the load at the remote point.

Let itnow be assumed that signals received by the primary I04 of transformer I02 shall be transmitted to audio amplifier I I8. It will be apparent that these signals will be transmitted from the remote point by secondary IOI, lead including capacitor 98, lead I03, low pass filter 9|, leads 51, 58, low pass filter I01, lead IIE including capacitor II5, leads III and H4, primary II2 of transformer II3, secondary Into the audio amplifier I I8. In other words, signals received at the remote point can be made audible at the control point by using the same wire connections as are employed to control the receiver by means of the transmitter. It will further be apparent that the two wire connections between transmitter and receiver can be employed to carry other or additional signals.

The modification according to Fig, 2 is distinguished from the control apparatus according to Fig. 1 in that the frequency output of oscillator 50 is controlled by impulse producing means rather than by a control unit comprising relatively movable control members. Th control of the load at the remote point by different frequencies and the arrangement of the receiver proper and of the back indicating means are the same as in Fig. 1. The same reference characters are used in both figures to designate similar or corresponding components.

It will also be evident that the arrangement of Fig. 2 lends itself to the use of radio channels instead of wire connections without departing from the spirit and scope of the invention.

Referring now to Fig. 2 in detail, the control apparatus according to this figure comprises a ratchet wheel I30 which can be rotated by means of a rotatabl knob I3I. A transmission I32 between wheel and knob is indicated b a dotted line. Wheel I 30, when rotated, rocks a flexible contact arm I34 vibrating about a point I35 between two stationary contacts I36 and I 31. A spring I38 biases arm I34 against contact I36 connected by lead 25 to source of D. 0. current 20, Contact I31 is connected by a lead I39, a capacitor I40 and a resistor I4I to arm I34. Contact I31 is further connected by a lead I42 to one terminal of the coil of a relay I43, the other terminal of the relay coil being connected by a lead I44 to supply lead 34. There are further provided a variable resistor I 45 and a capacitor I46 connected by leads I41 and I48 respectively in parallel to the relay coil. Armature I50 of relay I43 controls a relay contact I5I connected to oscillator lead I20. Armature I50 is disengaged from contact I5I when the relay is deenergized and is connected by a lead I52 to a contact spring I53. This contact spring coacts with two contact springs I54 and I55 both connected by leads I56 and I 51 to the second oscillator connection I2I. Leads I56 and I 51 include capacitors 53 and 54 for control of the oscillator frequencies as previously explained. -Contact' spring I53 is biased to be normally disengaged from either contact spring I54 and I55. For they purpose of flexing spring I53. into engagement with either one of springs I54 and I55, spring I53 is operatively connected through a. friction clutch I58 of conventional design to transmission I32. As a result, rotation of knob I'3I will cause spring I53 to engage either one of the springs I54-or' I55 depending upon the direction of rotation. 'The contact springs will remain in engagement as long as knob I3I and wheel 530 respectivel are rotated, the slipping of'clutch l58 permitting continued rotation of the knob and the wheel. I59 and E58 may be provided to limit the moveents of the contact springs. When the rotation of the knob and the wheel are discontinued,

spring contact I53 will return into its disengaged;

position due-to its springiness.

The operation of the control apparatusaccording to Fig. 2 is as follows:

Let it be assumed that knob I3I is rotated and that the nose of arm 35 comes to rest between two teeth of wheel 13%] so that arm E34 engages contact list. Let it be further assumed that the knob is rotated in such direction that contact spring 553 engages spring I54. As will be apparent, an energizing circuit is closed for relay 543' during the charging period of capacitor I45 which circuit may be traced through lead 25, contact I35, arm 34, resistor I4I, capacitor I48- lead I42, the relay coil, lead I44 and. lead 34 back to the source of current. closes contact II during the charging of capacitor Iiii), thereby connecting capacitor 53 to the oscillator through lead i253, contact l5l, armature I58, lead I52, spring I55, spring I54, leads I55 and IEI. As a result, oscillator 58 will'produce the frequency associated with capacitor 53 which frequency in turn will control the selective means of the receiver as previously. explainedin detail in connection witlr Fig. l. The charging current of capacitor I40 also causes charging of capacitor 45. The energizing current through the relay will cease when capacitor I46 is dis* charged.

As the rotation of wheel I3?) is continued, the next tooth of the wheel will orce arm I34 into a position engaging contact 37. Capacitor I48 is now discharged through resistor MI, arm I34 and lead I39 so that the apparatus is ready for a new impulse re-energizing relay I43:when contact I35 is re-engaged by arm i34.

As will be evident, the length of the impulses is controlled by the capacitance of capacitor I45 and also by the adjustment of resistor 45 or other components of the network. Any desired length of impulses can be attainedby adjusting the resistor accordingly and it is also quite practical to adjust the resistor in such manner that at a certain rate of rotation of knob I3 I or wheel 13D rela I43 remains energized between impulses. 1

Stops Consequently, relay I 43 appendedclaims, to cover all such 'changes and modifications.

What is claimed as-new and-desired tobe secured by Letters Patent is:

As will be apparent from the previous description, rotation of knob I3! permits faster or slower step by step movement of load 85 until the, same is placed in the selected positionwhich is back indicated as described in connection with Fig-,1.

While the invention has been described in dethe invention, and-itis intended therefore in the.

1. An electric control apparatus of the followup-type-for placing a useful load in any desired position comprising a pair of independently movable control members at a control point, drive means including a reversible pilot-motor for moving one of the members, the'other being otherwise movable, circuit meansincluding the con-- trol members andthe pilot motor for controlling the rotational direction thereof by the relative position of the control members, a reversible motor for moving the load at a remote point,

oscillating means at the control point capable of producing a plurality of different frequencies, second circuit means including the control members and the oscillating means for frequency control of th latter by the relative position of the control members, a plurality of selective means at the remote point, each responsive to a different one of the frequencies of the oscillat ing means, electric connections between the oscillating means and the selective means for control of the latter by. the oscillating means, and third circuit means including the-selective means and the load motor for controlling the rotational direction and the stopping thereof by the selective means, said pilot motor and said oscillating means being connected to be rendered inoperative for the purposes aforesaid. when said control members reach a predetermined position relative to each other.

2. An electric control apparatus of the followup type for placing ai-load in any desired position comprising a pair of independently movablecontrol members at a control point, one member including electrically conductive elements separated by a gap, the other member including a contact element for engaging the conductive elements, drive means including a reversible pilot-= motor for moving one of the members, the other being otherwise movable, circuit means including the movable member and the pilot motor for controlling the rotational direction of the latter by the relative position of the control members, a reversible motor for moving the load at a re--' mote point, oscillating meansat the control point r ,capable of producing two diilerent frequencies,

second circuit means including the control members and the oscillating means for energizing the latter with one or the other frequency corresponding to the relative position of the control members, a pair of selective means at the remote point, one of the selective means being responsive to one of said: frequencies and the second being responsive to the other frequency, electric connections between the oscillating means and the selective means for energizing one of the selective means as controlled by the frequency of the oscillating means, and third circuit means including the selective means and the load motor.

for controlling the rotational direction and the stopping thereof by the energized selective means,

said pilot motor and said oscillating means beingconnected to be renderedinoperative for the purpose aforesaid when the contactelement occupies the gap.

3. An electric control apparatus of the followup type for placing a useful loadin any desired position comprising apair of independently mov-- able control members at a control point, one member including electrically conductive elementsseparated by a gap,,the other element including a contact element for engaging the conductive elements, drive means including a reversible pilot motor for moving one of the members, the other being otherwise movable, circuit means including the control members and the pilot motor for controlling the rotational direction of the latter by the relative position of the control members, a reversible motor for moving the load at a remote point, oscillating means at the control point capable of producing a plurality of different frequencies, relay means including a pair of coils connected in circuits with respective ones of the conductive elements for energizing one or the other coil as controlled by the relative position of the control members, said relay means connected in circuits with the oscillating means for frequency control of the latter by the relative position of the control members, a plurality of selective means at the remote point, each responsive to a different one of the frequencies of the oscillating means, electric connections between the oscillating means and the selective means for nergizing the selective means responsive to a particular frequency produced by the oscillating means, and second relay means including a pair of coils connected with respective ones of the selective means for energizing one Or the other of said relay coils corresponding to the'energization of the respective selective means, said second relay means electrically connected with the load motor for controlling the rotational direction and the stopping of the latter by the second relay means, said pilot motor and said oscillating means being connected to be rendered inoperative for the purposes aforesaid when the contact element occupies the gap.

4. An electric control apparatus of the followup type for placing a useful load in any desired position comprising a pair of independently movable control members at control point, one member including electrically conductive elements separated by a gap, the other element including a contact element for engaging the conductive elements, drive means including a reversible pilot motor for moving one of the members, the other being otherwise movable, circuit means including the control members and the pilot motor for controlling the rotational direction thereof by the relative position of the control members, reversible motor for moving the load at a remote point, oscillating means at the control point capable of producing a plurality of different frequencies, second circuit means including the control members and the oscillating means for frequency control of the latter by the relative position ofthe control members, a plurality of selective means at the remote point, each responsive to a different one of the-frequencies of the oscillating means, electric connections between the oscillating means and the selective means for control of the latter by the oscillating means, third circuit means including the selective means and the load motor for controlling the rotational direction and the stopping thereof by the selective means, said pilot motor and said oscillating means being connected to be rendered inoperative for the purpose aforesaid when the said contact element occupies the gap, electric indicating means at the control point, a source of current included in a circuit with the indicating means through said. electric connections, and means for varying the amount of energy supplied to the indicating means corresponding to the position of the load for back indicating the load position.

5. An electric control apparatus of the followup type for placing a useful load in any desired position comprising a pair of independently movable control members at a control point, one member including electrically conductive elements separated by a gap, the other element including a contact element for engaging the conductive elements, drive means including a reversible pilot motor for moving one of th members, the other being otherwise movable, circuit means including the control members and the pilot motor for controlling the rotational direction thereof by the relative position of the control members, a reversible motor for moving the load at a remote point, oscillating means at the control point capable of producing a plurality of different frequencies, second circuit means including the control members and the oscillating means for frequency control of the latter by the relative position of the control members, a plurality of selective means at the remote point, each responsive to a different one of the frequencies of the oscillating means, electric connections between the oscillatin means and the selective means for control of the latter oy the oscillating means, third circuit means including the selective means and the load motor for controlling the rotational direction of the load motor and the stopping thereof by the selective means, said pilot motor and said oscillating means being connected to be rendered inoperative for the purposes aforesaid when the said contact element occupies the gap, electric indicating means at the control point connected with said electric connections, an independent source of current at the remote point connected with said electric connections, and electric means mechanically controlled by the load position for varying the amount of energy supplied to the indicating means from said source of current through said electric connections corresponding to the angular position of the load, thereby back indicating the load position.

6. An electric control apparatus of the followup type for placing a useful load in any desired position comprising a pair of independently movable control members at a control point, one

member including electrically conductive elements separated by a gap, the other element including a contact element for engaging th conductive elements, drive means including a reversible pilot motor for moving one of the members, the other being otherwise movable, circuit means including the control members and th pilot motor for controlling the rotational direction thereof by the relative position of the control members, a reversible motor for moving the load at a remote point, oscillating means at the control point capable of producing a plurality of different frequencies, second circuit means including the control members and the oscillating means for frequency control of the latter by the relative position of the control members, a plurality of selective means at the remote point, each responsive to a different one of the frequencies of the oscillating means, electric connections between the oscillating means and the selective means for control of the latter by the oscillating means, third circuit means including the selective means and the load motor for controlling the rotational direction of the load motor and the stop ping thereof by the selective means, said pilot motor and said oscillatin means being connected to be rendered inoperative for the purposes aforesaid when the said contact element occupies the gap, electric indicating means at the control point connected with said electric connections, an independent source of current at the .remote pointx connected with said electric connections, a potentiometerincluded in a circuit with the independentsource or" current, andtransmission means operatively connecting the .rnovable contact of said potentiometer with the load forvarying the amount of energy supplied. to the indicating means through said electric connections corresponding to the angular position of the load, thereby back indicating the load position.

'7. An electric control apparatus of the followup type for placing a useful load in any desired position comprisinga pair of independently movable control members at av control point,,one

member including electrically conductive elements separated by a gap, the other element including a contact element forengaging the conductive elements, drivemeans including .a re-.

versible pilot motor for moving one. of the members, the other being .otherwise movable, circuit means including the control members and the pilot motor for controlling the rotational direction thereof by the relativeposition of thecontrol members, a reversible motor for moving the load at a remote point, oscillating means at the control point capable of producing aplurality of diiferent frequencies, .second circuit means including the control membersand the oscillating means for frequency control of thelatter by the relative position .of the control members, a plurality of selective means at theremote point,.each

responsive to a different one .of the frequencies. of the oscillating means, electric connections be-.

tween the oscillating. meansand. the selective means for control of the latter by the. oscillating means, third circuit meansinoluding the selective means and the load motor forgcontrolling the rotational directionof the. ,load motor and .the.

motor andsaidoscillatingmeansbeing, connected 12. means. including'thecontrol. members and thv pilot -.motor for controlling the rotational" direc-w tion thereof by therelative position of the control members, a reversible motor for moving the load at a :remote point,oscillating means at the controlpointcapable of producing a plurality of dif-. ferent-frequencies, second circuit means includ- -f ing thencontrolv members and theoscillating means for frequency controlof the latter by the relative position of the control members, a pluralityzofselective means at the remote point, each responsive to a different one of the frequencies of the oscillating means, electric connectionsbetweenthe oscillating means andthe selective means-for control of the latter by the oscillating I meansthird circuit means including the sele"-- tive means and the load motor for controlling the rotational direction 'of the load motor and the stopping thereofby the selective means, said pilot motorand said oscillating means being connected to be rendered inoperative for the purposes aforesaid when: the said-contact element-occupies the gap,-electric means capable of receiving signals connected-at the remote point with said electric connections-for transmitting the said signals to thecontrol point, electric signal means responsive to the signals connected at the'control point with said electric connections, filter means included in said electric connections,- said filter means beingconstructed to block signal frequencies cor responding substantially to onecr" thev frequencies of the oscillating means to reach the selectiveineans, thereby preventing-such frequencies to afiectthezselective means, and second-filter means includedlin said electric connections, said second filter means constructed to blockirequencies originating in the oscillating means to reach the signal. means. stopping, thereof ,by the. selective means, said pilot.

to be rendered. inoperative forthepurposes aforesaidwhen the said contact element occupies the gap, electric means capable of receiving signals connected at the remotepoint withsaid electric connections for transmitting the said signals to the controlpoint, and electric signal means responsive to saidsignals connected at the control point with said electric connections.

8. An electriccontrol apparatus of the IEOHOW". up type for placing. auseful load in any desired position comprisingapair of independently movable control members at a control point,.one member including. electrically conductive. ele-.

mentsseparated by agap, the other element. in. cluding a contact element for engaging thev con-r ductive elements, drivemeans including a reversible pilot motor for moving one of the members, the other being otherwise movable, circuit MICHEL N. YARDENY. ROBERT BERNAS. SIMON GOLDBERG.

REFERENCES CITED The following references "are of record in the 

